In a high speed optical transmission system, a light emission module in a light transceiver plays an important role, especially a high-speed laser diode module with a speed higher than 25 Gbps. In this light emission module, a length of a connecting line between a laser diode and a laser diode driver seriously affects the quality of the signal transmission. Therefore, the shorter a distance between the laser diode and the laser diode driver is, the better the quality of the signal transmission is. In order to monitor the operation of the laser diode, which emits the laser from the front side and leaks a light from the rear side, a monitor photodiode is disposed at the rear side of the laser diode. The monitor photodiode detects the light leaked from the rear side of the laser diode so as to monitor the operation of the laser diode.
In the conventional light emission module, the monitor photodiode is disposed right behind the rear side of the laser diode for detecting the light leaked from the rear side of the laser diode. In order to prevent the light incident on a light receiving surface of the monitor photodiode from reflecting back to the laser diode, the light receiving surface of the monitor photodiode is tilted relative to an emission axis of the laser diode. In high-speed laser diode module, the laser diode and the laser diode driver are requested to be assembled in one module. In order to the distance between the laser diode and the laser diode driver, the laser diode driver is disposed at a lateral side of the laser diode which is between the front side and the rear side of the laser diode. However, the aforementioned arrangement provides an overly large width of the light emission module so that a size of the light transceiver is increased together with the width of the light emission module.